Urinary tract infections in men

Urinary tract infection (UTI) results from pathogenic organisms gaining access to the urinary tract and not being effectively eliminated. The bacteria ascend the urethra and generally have an intestinal origin. Escherichia coli is the most common pathogen in both men and women, although less common in men. One retrospective study found E coli infections to be significantly more frequent in females (53.2%) than in males (26.6%, P <0.001).[20]

Men, however, more frequently have UTIs associated with a varied group of causative organisms. This includes other gram-negative bacteria, such as Klebsiella, Proteus, and Providencia as well as non-fermenting bacteria, such as Pseudomonas, and gram-positive infections, such as enterococci or staphylococci.[5][8][21][22]

A 5-year study involving male veterans demonstrated that 40% of community-acquired infections and 55% of inpatient infections resulted from organisms such as Enterococcus and Staphylococcus.[23] For patients with catheter-associated UTI (CAUTI), the Centers for Disease Control states the three most common pathogens are E coli, Klebsiella, and P aeruginosa.[24] When a UTI develops in patients in hospitals or long-term care facilities or as the result of indwelling catheters, Candida and other multidrug-resistant organisms must be considered.[22][25][26]

UTI develops when the balance between host defence mechanisms and the virulence of the invading organism is distorted.[27] For example, men with immunodeficiency (e.g., diabetes, cancer, HIV) more often acquire UTI.[5][19] Another important defence mechanism is urine flow. Disruption of this defence and subsequent raised post-void residual can contribute to the development of UTI in men.[28]

Structural or functional abnormalities of the urinary tract that increase risk of UTI include:[22]

Prostate disorders
Calculi within the collecting system or the kidney
External drainage devices or internal devices such as stents
Urinary diversion surgeries
Vesicoureteral reflux
Neurogenic bladder disorders, including diabetes mellitus.

With ageing, the incidence of problems causing complicated UTI (cUTI) increases, and this corresponds to the increased incidence of UTI in older men. Structural or functional abnormalities of the urinary tract occur more frequently in older men.[29]

Healthcare-associated versus community-acquired

Healthcare-associated (nosocomial) UTI implies acquisition of the pathogenic organism from within a healthcare facility, whereas community-acquired infection occurs without exposure to such a facility.

Complicated

Previously guidelines have classified all UTIs in men as complicated UTIs but this has evolved with recent guidance. According to new classification in the 2025 IDSA guidelines, uncomplicated UTIs occur in afebrile male or female patients without known risk factors and are confined to the bladder, while all other UTIs fall into the category of complicated UTIs.[1][2] cUTI implies the presence of other factors that hinder the efficacy of therapy, such as:[3][4][5]

Structural or functional abnormalities of the urinary tract
Immunodeficiency
Indwelling catheter
Infection due to resistant organisms.

Localised

In 2025, the European Association of Urology proposed a new classification scheme for UTIs, moving away from the terms ‘uncomplicated’ and ‘complicated’ to emphasise the difference between localised and systemic UTIs.[2]

Localised UTIs are defined by cystitis without any signs and symptoms of systemic infection in either sex. Symptoms may include dysuria, urgency, frequency, incontinence, urethral purulence or pressure/cramping in the lower abdomen.[2]

Systemic

A systemic UTI is an infection with signs and symptoms of systemic infection with or without localised symptoms which originates from any site in the urinary tract in either sex. Symptoms/signs may include fever or hypothermia, rigours, delirium, hypotension, tachycardia, or cotovertebral angle pain/tenderness.[2]

Recurrent

Recurrent UTI is defined as having occurred at least three times in one year or as having two UTIs within 6 months.[2] This can result from persistence of an infection that is inadequately treated or the acquisition of a new infection.

Asymptomatic bacteriuria

Patients with ≥10⁵ CFU/mL in culture from a single specimen, but without dysuria, frequency, urgency, or suprapubic or costovertebral angle (CVA) pain, are classified as having asymptomatic bacteriuria.[6]

Pathophysiology

Classification